The invention relates to a parking and maneuvering valve for trailers having a spring-loaded parking brake.
The design of the standard brake system for trailers is a prior art brake system that is equipped with a spring-loaded parking brake that is in general complicated and expensive. A trailer brake valve is used that is connected to a so-called combination release valve. In addition, there is a separate two way or shuttle valve that prevents stress on the mechanical brake due to additional force from the service brake member and the spring-loaded brake member on the trailer brake. This class of brake system is provided with two button control. That is, the combination release valve works with two actuating buttons. When the trailer is uncoupled and braked, the combination cylinder, which combines the diaphragm cylinder/spring-loaded cylinder of the service brake and parking brake, can be released by depressing both buttons and thus, the unbraked vehicle can be moved.
Given the above, the object of the invention is to simplify in such a manner the construction of trailer brake systems, equipped with a spring-loaded parking brake, that it retains the two button control and yet is inexpensive. In principle, it should be possible to put the trailer into park position both in the coupled and uncoupled state even if, as a consequence of short term or long term leakages, pressure losses in the compressed air supply of the trailer must be accepted.
This problem is solved with the features according to the claimed invention.
The simple construction of the valve unit, which eliminates the additional use of a trailer brake valve, is achieved through a combination of release unit, parking unit, and emergency brake unit. The emergency brake unit automatically reduces the speed of the trailer in the event of a break in the supply line, not by means of the service brake of the trailer, but by means of the spring-loaded brake system, a feature that constitutes a significant contribution to the functionality and reliability of the trailer brake system to the effect that during emergency braking no compressed air supply is necessary to operate the service brake and short or long term leakages in the compressed air supply of the trailer do not have any negative effect on the braking during standstill. The module, comprising release unit, parking unit and emergency brake unit, forming preferably a valve block, has universal application. It can also be retrofitted. If the two button control is kept, then previously recognized advantages of the control mode and possibilities can be retained.
Advantageous embodiments and improvements are described herein.